This invention relates to coated, paperboard containers and in particular to containers for packaging and storing materials which are prone to leak from the containers or to damage the paperboard by seeping through minor cuts and imperfections in the coating on the paperboard.
Paperboard containers for a great variety of foods and beverages have become widely known and utilized. For example, containers such as those disclosed in U.S. Pat. No. 2,750,095 have been employed for holding perishable foods for relatively short periods of time, on the order of about two weeks. Such containers have found wide applicability for beverages, such as milk and orange juice. Typically, such containers have been assembled from a paperboard blank, coated on both sides with one or more layers of a protective, thermoplastic material, such as polyethylene. Such containers have provided substantial advantages in both economy and convenience for producers as well as consumers.
However, the use of such containers over an extended period of time with certain penetrative fill products has raised certain significant problems. One problem has involved the relative lack of durability of such containers when holding liquids and syrups for longer than a few weeks. The fluid contents of such containers have usually tended to "wick" or seep through damaged areas of or defects in the thermoplastic coating into the paperboard base stock. This seepage of fluid through the inside, thermoplastic coating into the paperboard has tended to weaken the containers and to cause them to ultimately leak or rupture.
It has been found that wicking occurs principally at certain sites, inside the containers. Usually, such sites are where the paperboard material has been scored, folded and/or flexed in forming blanks for containers, folding the blanks along the score lines to form the containers, or in filling, closing or storing the containers. In the case of some diet, soft drink syrups, it has been noted that almost any damage to the coating material on the inside surface of the containers can result in rapid and disastrous penetration of the paperboard base stock by the syrup. Obviously, this problem is particularly aggravated when the containers are stored for a relatively long period of time, since exposure of even small areas of the paperboard base stock, such as may occur through tiny pin holes in the thermoplastic coating, can, over a long period of time, cause the wicking of the fill product into substantial portions of the paperboard base stock and the resulting failure of the containers.
In addition to the problem of the durability of paperboard containers for liquids, another obvious problem has been the relative lack of adequate protection for the quality of the material packaged in such containers over a relatively long period of time. Typically, a substantial loss of quality has been encountered when utilizing conventional paperboard containers for holding liquid materials for more than about two weeks. This has been due primarily to the inadequacy of conventional thermoplastic coating materials as barriers against the loss of aromatic oils and other ingredients vital to the flavor of various substances. Loss of quality has also been attributed to the fact that conventional thermoplastic coatings are relatively inadequate barriers against penetration by gases such as oxygen.
In order to overcome such problems in paperboard containers, coated laminates of paperboard and aluminum foil have been utilized. See, for example, U.S. Pat. No. 3,365,111. The aluminum foil, when bonded to the paperboard, has been found to enhance the durability of the resulting containers by inhibiting the liquid or syrup contents from penetrating the paperboard base stock. More importantly, the aluminum foil has served as an effective barrier against both the inflow and outflow of gases and liquids, thereby minimizing the deterioration of the contents of the containers over prolonged periods.
Aluminum foil-paperboard laminated have not, however, been entirely satisfactory for some fill products. The containers made from such laminates have still been prone to wicking through score cuts, breaks or defects in the thermoplastic material and aluminum foil into the paperboard base stock, particularly over extended periods of time. Although the amount of wicking has been reduced with such laminates, the problem has continued to be a significant one when the containers have been used for some fill products over periods of about 2 months or more.
The problem of seepage through score cuts, breaks or defects in the thermoplastic coating and the aluminum foil has been a particularly serious problem at the corners of paperboard containers. At the corners, the paperboard laminates have been particularly susceptible to the effects of scoring and folding operations to form the containers, as well as the effects of flexing the container during the filling, conveying and packing of the containers. In this regard, it has been found that the aluminum foil is almost invariably crushed or cracked during the scoring and folding of the paperboard blanks, rendering the containers susceptible to the deleterious effects of fluid leakage into the paperboard base stock.
There has been an unfilled need therefore for a paperboard laminate material having improved abuse resistance, particularly resistance to the effects of scoring, folding and flexing, and which also possesses barrier properties for maintaining the quality of the containers' contents over relatively extended periods of time.